This invention pertains to the radio control art and, more paticularly, to a channel selector system which sequentially accesses one of a plurality of radio channels as by either stepping or scanning sequentially through the channels and rapidly scans through any restricted or illegal channels until the next unrestricted channel is accessed to give the appearance to the radio operator that such restricted channels are skipped and to avoid display of any restricted channels.
It is common in certain communications bands to restrict the usage of certain channels within that band. Certain channels may also be limited to certain operating modes, such as receive only. For example, in the United States the domestic marine channels are in the 156.0 to 162.5 MHz band. Channels 1 through 4 are weather channels and are restricted to receive only operation. That is, no transmission is permitted on these channels. Certain other channels, such as channels, 5, 29-64, 75 and 76, and 89-99 are reserved for various other purposes, such as for coast guard operations, and are restricted in both receiving and transmitting.
Some prior art marine radios utilize individual crystals for each desired channel. Such radios are limited to receiving or transmitting only those channels which have been implemented by the associated frequency crystal. There was therefore no problem of accessing a restricted channel since the radio could only receive or transmit on the implemented channels and crystals for the restricted channels were generally unavailable to the public.
More recently, frequency synthesizers have been utilized to generate the frequencies to enable receiving or transmitting on a plurality of channels within the communication band. The frequency synthesizer eliminates the need for a separate and individual crystal for each of the center frequencies of the desired channels. Sequential scanning or generating circuits are commonly employed to serially advance the frequency synthesizer from one channel to an adjacent channel in either an up mode (increasing channel numbers) or in a down mode (decreasing channel numbers). In so doing, the numbers of restricted channels as well as unrestricted channels are often displayed. While the radio may be coded to prevent reception or transmission on the restricted channels, there is the possibility that reception or transmission on restricted channels may occur due to receive malfunction or due to illegal modification of the receiver to achieve this capability. Furthermore, a significant amount of time and operator inconvenience may be entailed in serially advancing from the last unrestricted channel through a plurality of restricted channels to the next unrestricted channel. For example, to advance from channel 28 to the next unrestricted channel 65 requires advancing through 36 restricted channels, namely channels 29-64.